The beneficial use of phospholipases and lipases (referred to as lipolytic enzymes, (EC. 3.1.1.x) used in food and/or feed industrial applications has been known for many years.
For instance, in EP 0 585 988 it is claimed that lipase addition to dough resulted in an improvement in the antistaling effect. It is suggested that a lipase obtained from Rhizopus arrhizus when added to dough can improve the quality of the resultant bread when used in combination with shortening/fat. WO94/04035 teaches that an improved softness can be obtained by adding a lipase to dough without the addition of any additional fat/oil to the dough. Castello, P. ESEGP 89-10 December 1999 Helsinki, shows that exogenous lipases can modify bread volume.
Lipolytic enzymes hydrolyse one or more of the fatty acids from lipids present in the food which can result in the formation of powerful emulsifier molecules within the foodstuff which provide commercially valuable functionality. The molecules which contribute the most significant emulsifier characteristics are the partial hydrolysis products, such as lyso-phospholipids, lyso-glycolipids, and mono-glyceride molecules. The polar lipid hydrolysis products, such as lyso-phospholipids and lyso-glycolipids are particularly advantageous. In bread making, such in situ derived emulsifiers can give equivalent functionality as emulsifiers, such as DATEM.
However, the activity of lipolytic enzymes also results in accumulation of free fatty acids, which can lead to detrimental functionality in the foodstuff. This inherent activity of lipolytic enzymes limits their functionality.
Numerous solutions to this problem have been attempted in the art. However, these result in a significant increase in free fatty acids in the foodstuff, particularly food stuffs with high water content, including, but not limited to bread doughs and egg yolk.
Phospholipases, particularly phospholipase A2 (E.C. 3.1.1.4), have been used for many years for the treatment of egg or egg-based products (see U.S. Pat. No. 4,034,124 and Dutihl & Groger 1981 J. Sci. Food Agric. 32, 451-458 for example). The phospholipase activity during the treatment of egg or egg-based products results in the accumulation of polar lysolecithin, which can act as an emulsifier. Phospholipase treatment of egg or egg-based products can improve the stability, thermal stability under heat treatment such as pasteurisation and result in substantial thickening. Egg-based products may include, but are not limited to cake, mayonnaise, salad dressings, sauces, ice creams and the like. Use of phospholipases results in the accumulation of free fatty acids. The accumulation of free fatty acids can result in significant off-flavour. In addition, the accumulation of free fatty acids can result in enhanced susceptibility to oxidation, and hence result in poor shelf-life, product discoloration and alteration of other critical food characteristics such as flavour and texture. Recently, lipolytic enzymes with broader substrate specificity have been marketed for treatment of egg yolk and related food products. These have the advantage that, unlike most of the phospholipase A2s, they do not originate from a mammalian source. However, they result in significant accumulation of free fatty acids, not only due to the hydrolysis of phospholipids, but also triglycerides.
As mentioned above, another area where lipases have been extensively used is in the bakery industry. The use of phospholipases in baking dates bake to the early 1980s.
The substrate for lipases in wheat flour is 1.5-3% endogenous wheat lipids, which are a complex mixture of polar and non-polar lipids. The polar lipids can be divided into glycolipids and phospholipids. These lipids are built up of glycerol esterified with two fatty acids and a polar group. The polar group contributes to surface activity of these lipids. Enzymatic cleavage of one of the fatty acids in these lipids leads to lipids with a much higher surface activity. It is well known that emulsifiers, such as DATEM, with high surface activity are very functional when added to dough.
However, the use of lipases (E.C. 3.1.1.X) in dough products may have a detrimental impact on yeast activity, and/or a negative effect on bread volume. The negative effect on bread volume is often explained by overdosing. Overdosing can lead to a decrease in gluten elasticity which results in a dough which is too stiff and thus results in reduced bread volumes. In addition, or alternatively, such lipases can degrade shortening, oil or milk fat added to the dough, resulting in off-flavour in the dough and baked product. Overdosing and off flavour have been attributed to the accumulation of free fatty acids in the dough.
In EP 1 193 314, EP 0 977 869 and also in WO 01/39602, the use of lipolytic enzymes active on glycolipids was reported to be particularly beneficial in application in bread making as the partial hydrolysis products the lyso-glycolipids were found to have very high emulsifier functionality, apparently resulting in a higher proportion of positive emulsifier functionality compared to the detrimental accumulation of free fatty acids. However, the enzymes were also found to have significant non selective activity on triglyceride which resulted in unnecessarily high free fatty acid.
The same finding was reported in WO 00/32758, which disclosed lipolytic enzyme variants with enhanced activity on phospholipids and/or glycolipids, in addition to variants which had a preference for long rather than short chain fatty acids. This latter feature, also disclosed in WO 01/39602, was deemed of particular importance to prevent the off-flavours associated with the accumulation of free short chain fatty acids. However, significant free fatty acids are produced.
The problem of high triglyceride activity was addressed in WO02/094123, where the use of lipolytic enzymes active on the polar lipids (i.e. glycolipids and phospholipids) in a dough, but substantially not active on triglycerides or 1-mono-glycerides is taught. However, significant free fatty acids are produced.
Some lipolytic enzymes have low or no activity on the lyso form of polar lipids (e.g. glycolipids/phospholipids). The use of such enzymes has been deemed preferable as they ensure the accumulation of the highly polar lyso-lipids, resulting in optimal functionality. Free fatty acids do however accumulate. This selective functionality is characteristic of phospholipase A2 enzymes, and the glycolipases disclosed in EP 0 977 869, EP 1 193 314, and WO01/39602. Variant enzymes of less selective lipolytic enzymes have been produced which have a lower activity on the lyso-polar lipids when compared to the parent enzyme (WO03/060112). However, significant free fatty acids are produced.
WO00/05396 teaches a process for preparing a foodstuff comprising an emulsifier, wherein food material is contacted with an enzyme such that an emulsifier is generated by the enzyme from a fatty acid ester and a second functional ingredient is generated from a second constituent. WO00/05396 teaches the use of in particular a lipase or esterase enzyme. Nowhere in WO00/05396 is the specific use of a lipid acyltransferase taught. In addition, in foodstuffs with high water content, the use of the esterases and lipases as taught in WO00/05396 would result in significant accumulation of free fatty acids.
A disadvantage associated with the use of lipases, including phospholipases and glycolipases, may be caused by the build-up of free fatty acids released from the lipids. Over the past couple of decades the use of lipolytic enzymes in foodstuffs has been limited due to the balance between the detrimental accumulation of free fatty acids and the production of the lyso-lipids which provide positive functionality. Although numerous strategies in the art have been attempted, some of which provided significant improvements in functionality, none have completely addressed and solved the fundamental problem in the art, i.e. the significant accumulation of free fatty acids in foodstuffs prepared using lipolytic enzymes in situ.
The presence of high levels of free fatty acids (FFA) in raw materials or food products is generally recognised as a quality defect and food processors and customers will usually include a maximum FFA level in the food specifications. The resulting effects of excess FFA levels can be in organoleptic and/or functional defects.
A result of lipolysis is hydrolytic rancidity, with the formation of characteristic “soapy” flavour. This “soapy” taste is especially acute with fatty acids of intermediate chain length (C8-C12) which, although not present in high concentrations, may be important constituents of, for example, dairy products or vegetable oils. A more common organoleptic defect is due to the combined effects of lipolytic enzymes and oxidation processes. Unsaturated fatty acids are more susceptible to enzymatic oxidation when unesterified than when esterified in acyl lipids.
Functional defects in food due to high FFA levels are recognised, but less readily explained. Without wishing to be bound by theory, the hydrolysis of unchanged lipids to carboxylic acids will increase [H+] and produce carbonyl groups that can combine with other compounds or metal ions. Free fatty acids also combine proteins by hydrophobic interactions and can complex with starch during cooking. FFA may also interfere with the action of surface-active agents, such as polar lipids and emulsifiers. (Lipid in Cereal Technology, P. J. Barnes, Academic Press 1983.)
WO03/100044 discloses a class of acyl transferases known as PDATs (or ATWAX). These enzymes use a monoglyceride or a diglyceride as the acceptor molecule, and phosphatidylcholine (PC) as the donor molecule to produce the following products: lyso phosphatidylcholine and triacylglycerol and/or diacylglycerol.
In one embodiment, the present invention relates to improvements in the incorporation of whey proteins into food products, providing for improved yields without impairing the qualities—such as the texture—of the food compositions and products.
Cheese compositions are typically prepared from dairy liquids by processes that include treating the liquid with a coagulating or clotting agent. The coagulating agent may be a curding enzyme, an acid or a suitable bacterial culture, or it may include such a culture. The curd that results generally incorporates transformed casein, fats including natural butter fat, and flavourings that arise especially when a bacterial culture is used. The curd may be separated from the liquid whey, which contains soluble proteins not affected by the coagulation and that therefore are not incorporated into the curd.
Whey is thus a by-product of manufacturing in commercial processes that produce food products—such as cheeses. Traditionally, whey is disposed of as unused waste or used as fertiliser or animal feed or processed into a food ingredient.
The inability of whey proteins to be substantially retained in the curd is an important factor contributing to a lack of efficiency in the conventional production of dairy products—such as cheese curds—and to a reduction in overall yield relating to the incorporation of all the protein solids that are present in the starting dairy liquids into resulting cheese curds.
There have been numerous attempts to include whey proteins in cheese e.g. by heat treatment of the milk, heat treatment of whey, or by filtration—such as ultrafiltration.
There are also several descriptions of the use of specific proteases to induce aggregation of whey proteins. A serine protease derived from Bacillus licheniformis has been shown to have the ability to induce aggregation of whey proteins (U.S. Pat. No. 5,523,237).
However, there remains many difficulties associated with adding whey proteins in processes such as the manufacture of cheeses. For example, incorporation of whey protein into cheeses is associated with a deterioration in the taste and mouth-feel of the product, and furthermore tends to interfere with curding and subsequent processing of the product. Proteases that have been previously reported that can be added to cheese milk for hydrolysis of whey proteins result in significant hydrolysis of the caseins as described by Madsen, J. S. & Qvist, K. B. (1997) Hydrolysis of milk protein by a Bacillus licheniformis protease specific for acidic amino acid residues. J Food Sci. 62, 579-582.
Thus, there is a need in the art for methods and compositions that provide for the improved incorporation of whey protein into food products while maintaining organoleptic and other desirable properties. Such optimisation would result in increased efficiency, higher yields of food products, and reduced overall material costs.
Lipase:cholesterol acyltransferases have been known for some time (see for example Buckley—Biochemistry 1983, 22, 5490-5493). In particular, glycerophospholipid:cholesterol acyl transferases (GCATs) have been found, which like the plant and/or mammalian lecithin:cholesterol acyltransferases (LCATs), will catalyse fatty acid transfer between phosphatidylcholine and cholesterol.
Upton and Buckley (TIBS 20, May 1995 p 178-179) and Brumlik and Buckley (J. of Bacteriology April 1996 p 2060-2064) teach a lipase/acyltransferase from Aeromonas hydrophila which has the ability to carry out acyl transfer to alcohol acceptors in aqueous media.